The San Francisco area tends to be hottest in Sept/Oct. Why is that,
since most places in the US are hottest in June - August? Is it just
the wind coming from the SW?

I just moved to LA and discovered the term June gloom - apparently
June tends to be overcast here. The past few days the high here was
99!

I also lived in the midwest once and June-Aug also was the hottest and
also had thunderstorms in the night.